How can I relate an entity with itself via ManyToMany? - php

Question

My entity "Documents" is related to different entities like for example "members", "products" or "projects" .
In my mySQL database this creates tables like:
documents_members
documents_products
documents_projects
Now I tried to create a relation with manytomany from documents to documents. So I added documents manytomany and I expect this table in my database:
documents_documents
This is my approach:
namespace App\Entity;
use Doctrine\Common\Collections\Collection;
use Doctrine\ORM\Mapping as ORM;
use Doctrine\Common\Collections\ArrayCollection;
use Symfony\Component\Serializer\Annotation\Groups;
/**
* #ORM\Entity(repositoryClass="App\Repository\DocumentsRepository")
*
*/
class Documents {
/**
* #ORM\Id()
* #ORM\GeneratedValue()
* #ORM\Column(type="integer")
* #Groups("documents")
*/
private $id;
/**
* #ORM\ManyToMany(targetEntity="Products", inversedBy="documents")
* #ORM\JoinColumn(name="products", referencedColumnName="id")
* #Groups("documents")
*/
private $products;
/**
* #ORM\ManyToMany(targetEntity="App\Entity\Projects", inversedBy="documents")
* #Groups("documents")
*/
private $projects;
/**
* #ORM\ManyToMany(targetEntity="App\Entity\Members", inversedBy="documents")
* #Groups("documents")
*/
private $members;
/**
* #ORM\ManyToMany(targetEntity="App\Entity\Documents", mappedBy="documents")
*/
private $documents;
}

Answer 1

You need to have both sides of the relationship mapped.
Each document links to several other documents, and many other documents may link to this one.
Something like this:
/**
* Many Documents link to many Documents.
* #ORM\ManyToMany(targetEntity="App\Entity\Documents", inversedBy="linkedFromDocuments")
* #ORM\JoinTable(name="document_links",
* joinColumns={#ORM\JoinColumn(name="link_origin", referencedColumnName="id")},
* inverseJoinColumns={#ORM\JoinColumn(name="link_destination", referencedColumnName="id")}
* )
*/
private $linkedDocuments;
/**
* #ORM\ManyToMany(targetEntity="App\Entity\Documents", mappedBy="linkedDocuments")
*/
private $linkedFromDocuments;
This will create a table named document_links, with two columns: link_origin and link_destination. On each of these columns there will be a foreign key pointing back to documents.
Note that the relationship is bi-directional. So you may have document#1 linked to document#2, and also document#2 pointing to document#1 (two distinct rows in the join table). Your application may want to account for that.